ON ABSORPTION SPECTRA AND CHEMICAL CONSTITUTION, 209 



vexed question of the constitution of these substances. Some of the 

 substances of a simple constitution belonging to this group had been 

 previously examined. 



W. A. Miller and also L. Soret proved the transparency of hydrocyanic 

 acid and the cyanides,^ and Hartley, independently, found that hydrocyanic 

 acid is a remarkably diactinic substance which exhibits no trace of 

 selective absorption.'-^ Cyanuric acid, owing to difficulties in its exami- 

 nation, arising out of its sparing solubility and the necessity for examining 

 warm solutions, at first appeared to give evidence of selective absorption. 

 It was subsequently proved, however, that there was no absorption band 

 even in layers of liquid 200 mm. thick, but that the rays between wave- 

 lengths 3330 and 2572 — that is, to where the spectrum was sharply cut 

 off — were only feebly transmitted.^ 



In the present research some derivatives of cyanic acid have been 

 included, but attention has been directed chiefly to cyanuric acid, melam- 

 ine, and their respective alkyl derivatives. 



The derivatives of cyanic acid which were examined are highly 

 diactinic and show only general absorption. 



Cyanuric acid is commonly represented as a closed chain compound 

 in which the chain is formed of alternate atoms of carbon and nitrogen 

 united by alternate double and single bonds (Formula I. ), and a similar 

 structure is assigned to the methyl ester (methyl cyanurate ; m.p. 135°), 

 which is obtained from cyanuric chloride by the action of sodium 

 methylate. The methyl ester (methyl iso-cyanurate, methyl tricarbimide ; 

 m.p. 175°), on the other hand, which is prepared by the distillation of 

 potassium cyanate with potassium methyl sulphate, is represented as a 

 derivative of iso-cyanuric acid (Formula II.), which contains three keto- 

 groups and has the carbon and nitrogen atoms united by single bonds 

 only. In this ester the alkyl radicals are directly united to the nitrogen 

 atoms. 



Formula I. Formula IT. 



HO.C : N.C.OH OC.NH.CO 



I II 11 



N : C.N HN.CO.NH 



I 

 OH 



Cyanuric acid. Iso-cyanurio acid or 



tricarbimide. 



Pyridine and dimethylpyrazine, in which there are carbon and nitrogen 

 atoms united by alternate double and single bonds, exhibit strong and 

 persistent absorption bands, the selective absorption being more pro- 

 nounced in dimethylpyrazine,^ which contains two nitrogen atoms, than 

 in pyridine, which contains only one. It was therefore to be expected 

 that substances possessing the constitution assigned to normal cyanuric 

 acid and its esters would likewise exhibit marked selective absorption, 

 and that even to a greater extent than dimethylpyrazine. 



On the other hand it was to be anticipated that the alkyl derivatives 



' Pkil. Tram., 1862, pp. 861-887 ; J. Chcm. Soc, vol. ii. p. 68 ; Arcli. des Sciences 

 Fhys., Geneva, 61, 1878. 

 . ^ Trans. Chem. Soc, 1882, 41, p. 45. = Proc. Clem. Soc, 1899, 15, p. 46. 



* Trans. Chzm. Soc, 1900, 77, 846. 

 1901, P 



